I have released a new version of my x86 performance-monitoring
counters patch for Linux. From the README:

Latest Updates
--------------
1999-10-25
- Version 0.7 with support for Linux kernels 2.3.22 and 2.2.13.
- The AMD K7 Athlon should now work properly.
- User-space now uses mmap() to read the kernel's accumulated
  counter state.
- The driver is now invoked via a new sys_perfctr() system call,
  instead of abusing prctl().
- The kernel patch has been cleaned up. The "#ifdef CONFIG_PERFCTR"
  mess has been eliminated.

This and future versions of this package can be downloaded from
http://www.csd.uu.se/~mikpe/linux/perfctr/

Planned enhancements in future versions include lazy update of
the control registers, global-mode counters, and routing counter
overflow to the local APIC.


/ Mikael Pettersson